Date Approved


Graduate Degree Type


Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

George Arnould

Academic Year




Jaw tracking is the process of the collimator jaws dynamically following the multileaf collimators during modulated therapy. Jaw tracking can be used throughout the dosimetry treatment planning process for IMRT and VMAT treatment plans. It can reduce a patient’s OAR dose by reducing low dose spillage from MLC interleaf leakage. This study aims to investigate if jaw tracking reduces OAR dose while maintaining PTV coverage in prostate patients with involved lymph nodes using 6MV VMAT treatment planning technique.


This is a quantitative study of 10 patients. For each patient, two plans were created, one plan using a non-jaw tracking technique, and the other plan incorporating a jaw tracking technique. Volumetric OAR doses, overall PTV coverage, Gradient Index, Conformity Index, and Homogeneity Index were recorded for both plans, and a dosimetric comparison was performed. Results were evaluated using the Wilcoxon signed-rank test.


Results of this study indicated statistically lower OAR dose on the JT plans than on non-JT plans. The bladder constraint doses were lower on the JT plans. The rectum constraint doses for the JT plans were statistically lower than the non-JT plans. The right and left femoral heads doses were lower on the JT plans than the non-JT plans. The max dose for the bowel bag and sigmoid colon were statistically lower for the JT plans. While the PTV 7020 and PTV 4680 coverage was lower for the JT plans compared to the non-JT plans.


A dosimetric reduction was found for most OAR dose constraints for the JT technique, providing better OAR sparing to help reduce organ toxicities. Using this technique, however, resulted in reduced coverage to the PTV 4680 and PTV 7020 volumes.